Stainless steel ERW pipes

1.What is Stainless Steel ERW Pipes?

Stainless Steel ERW Pipes(SS ERW pipe) are produced from stainless steel raw materials using the Electric Resistance Welding (ERW) process. Stainless steel pipes are known for their exceptional corrosion resistance and durability, making them a preferred choice in various industries. On the other hand, ERW pipes are ERW pipes are a type of welded steel tube and manufactured using a high-frequency electrical current to weld the seams of the pipe, offering cost-effectiveness and efficiency in production. When these two elements combine, Stainless Steel ERW Pipes deliver the corrosion resistance of stainless steel with the manufacturing efficiency of the ERW process.

Stainless steel pipes, composed primarily of iron with a minimum of 10.5% chromium content, resist corrosion and staining and provide a sleek, attractive appearance. ERW pipes, on the other hand, are produced by forming strips or coils of steel into a cylindrical shape and welding the longitudinal seam using the ERW process. This method ensures a strong, durable bond while allowing for efficient mass production.

In summary, Stainless Steel ERW Pipes are the result of welding stainless steel materials using the ERW process, offering the corrosion resistance of stainless steel combined with the cost-effectiveness and efficiency of ERW pipe manufacturing.

2.Manufacturing Process of Stainless Steel ERW Pipes
(1)Material selection
Cold-rolled stainless steel strip is used as raw material, and the surface condition is BA grade. Before the steel belt is used in the factory, the steel belt must be inspected in detail. Inspection items include: thickness, width, edge quality status, appearance and physical performance inspection. When necessary, the grain size of the raw materials must be inspected, and they can only be used for production after passing the inspection.

(2)Open the book
Before the steel strip enters the welded pipe unit, it is necessary to use a steel strip uncoiler to unroll the steel strip. For the final steel strip, a leveling mechanism needs to be added to level the steel strip to ensure that the steel strip enters the welded pipe unit in a straight state. The forming part successfully completes the bending and forming of the steel strip.

(3)Tube blank forming
Using continuous roll bending forming equipment, the steel strip is continuously rolled and deformed to make an open tube blank. The steel strip needs to pass through the joint action of the introduction module, rough rolling module and closing module of the welded pipe unit. Each module uses different types of rollers to bend different parts of the steel strip. Finally, the steel strip is gradually transformed from a flat surface. Bend to form an open tube blank, ready for welding into stainless steel tubes.

(4)Welding
Electric Resistance Welding (ERW) is employed to join the edges of the stainless steel strip or coil longitudinally. A high-frequency electrical current is passed through the edges of the material, causing them to heat up and fuse together under pressure, forming a strong weld.

(5)Weld leveling
Due to the impact of the welding current and the influence of gravity, the internal welds of stainless steel product pipes will protrude and the external welds will also be dented. These problems will not have an impact if used in ordinary low-pressure fluid environments. If used in a high-temperature, high-pressure, high-speed fluid environment, it will cause usage problems. Special weld leveling equipment must be used to eliminate this defect.

(6)Online heat treatment
During the roll bending process of the steel strip, work hardening will occur, which is not conducive to the later processing of the pipe, especially the bending process. During the welding process, there will be welding stress at the weld, which will cause cracking risks during later use, which requires heat treatment.

The commonly used heat treatment process at present is bright solution treatment under a hydrogen protective atmosphere. The 304 stainless steel pipe is heated to above 1050°. After a period of heat preservation, the internal structure morphology changes to form a uniform austenite structure. In the hydrogen atmosphere Under the protection of atmosphere, no oxidation will occur.

(7)Sizing and finishing
The outer diameter of the stainless steel ERW welded pipe will deform during the welding and heat treatment process, causing the outer diameter to fail to meet the usage requirements and requires sizing and finishing. The commonly used sizing and finishing unit consists of 4 sets of flat rollers and 4 sets of side rollers. The flat rollers are designed to be flat oval (or circular), and the side rollers are designed to be oval (or circular). The sizing amount depends on the outer diameter and wall thickness of the pipe, and is generally in the range of 0.20~0.50mm. After sizing and finishing, the outer diameter tolerance of the pipe can be controlled within ±0.05mm, which can fully meet the accuracy requirements.

(8)Online flaw detection
Due to the fact that it is subject to a certain amount of pressure and requires a certain degree of reliability, it is difficult to detect internal defects in stainless steel ERW welded pipe welds by relying only on pressure detection. Online eddy current flaw detection or ultrasonic flaw detection can be used to perform 100% detection online in real time. The welding status can be corrected at any time based on the alarm information to reduce the production of unqualified products.

(9) Cutting to length
Use online fixed-length cutting equipment to perform fixed-length cutting according to the length required by the customer. You can use rotary cutting (chipless) technology. Compared with chip cutting, chipless cutting has the characteristics of no cutting burrs and does not need to be performed in the later stage. Deburring of ports.

(10)Straightening
The straightness of the welded pipes produced by the roll bending unit cannot meet the usage requirements. Generally, the straightness of such welded pipes needs to be controlled at 0.10/100mm. It is necessary to use a straightening machine to straighten the welded pipe to meet the required product requirements.

(11)Stress test
An automatic static hydraulic pressure testing machine is used to perform a pressure test on stainless steel ERW welded pipes. Loading, flushing, pressure testing, and unloading are all completed automatically. After maintaining pressure for a certain period of time, unqualified welded pipes are sorted out by the pressure difference method.

(12) Clean and dry
After the mechanical processing of stainless steel ERW welded pipes, final cleaning and drying are required to remove residual coolant, oil and other pollutants on the inner or outer walls of the pipes, and then hot air drying is used to prevent rust during transportation and storage. Finally, the finished stainless steel welded pipes are inspected and packaged before leaving the factory.

3. Comparison of Stainless Steel Grades: 317L, 310, 316H, and 304 ERW Pipes
When comparing Stainless Steel Grades 317L, 310, 316H, and 304 ERW Pipes, several factors come into play, including their chemical composition, mechanical properties, corrosion resistance, and applications.

(1)Stainless Steel Grade 317L ERW Pipe

Firstly, Stainless Steel Grade 317L is a low-carbon version of Grade 317, offering improved corrosion resistance in highly corrosive environments due to its higher molybdenum content. It exhibits excellent resistance to a wide range of chemicals, acids, and chlorides, making it suitable for applications in chemical processing, pulp and paper, and pharmaceutical industries. Additionally, 317L ERW pipes offer enhanced creep and stress rupture properties at elevated temperatures.

(2)Stainless Steel Grade 310 ERW Pipe

Stainless Steel Grade 310 is characterized by its high chromium and nickel content, along with its excellent oxidation resistance at high temperatures. Grade 310 ERW pipes are commonly used in applications requiring resistance to high-temperature environments, such as heat treatment furnaces, kilns, and thermal processing equipment. Its high chromium content provides good resistance to oxidation and sulfidation, while its high nickel content enhances its corrosion resistance in reducing environments.

(3) Stainless Steel Grade 316H ERW Pipe
Stainless Steel Grade 316H is an austenitic stainless steel with high carbon content, offering improved high-temperature strength compared to Grade 316. It exhibits excellent corrosion resistance in various corrosive environments, particularly in acidic and chloride-containing solutions. Grade 316H ERW pipes are widely used in industries such as chemical processing, marine, and oil and gas, where corrosion resistance and high-temperature strength are critical requirements.

(4) Stainless Steel Grade 304 ERW Pipe
Stainless Steel Grade 304 is one of the most commonly used austenitic stainless steels, known for its versatility, corrosion resistance, and ease of fabrication. Grade 304 ERW pipes offer good corrosion resistance in mildly corrosive environments and are suitable for a wide range of applications, including food and beverage processing, architectural, and sanitary applications. However, Grade 304 may exhibit sensitization when exposed to high temperatures for extended periods, leading to intergranular corrosion in certain environments.

In summary, while all four stainless steel grades—317L, 310, 316H, and 304—offer excellent corrosion resistance and mechanical properties, their specific compositions and characteristics make them suitable for different applications. Grade 317L provides enhanced corrosion resistance in highly corrosive environments, Grade 310 offers excellent oxidation resistance at high temperatures, Grade 316H provides improved high-temperature strength, and Grade 304 offers versatility and ease of fabrication in a wide range of applications. When selecting the appropriate grade for a specific application, factors such as temperature, corrosive environment, mechanical requirements, and cost considerations should be taken into account.